Elastomer insulation compositions for rocket motors

ABSTRACT

Non-asbestos elastomeric insulation materials for rocket motors are disclosed. The insulation materials comprise 100 parts by weight of a crosslinked elastomer polymer and between about 10 and 100 (preferably 15-75) parts by weight of an organic fiber selected from cotton flock, Sisal and a combination of cotton flock and Sisal. The insulation materials have notable erosion resistance and can be tailored to have thermal, mechanical and other properties of desired character. The organic fiber advantageously functions as a char forming, low density filler. Other ingredients such as silica, phenolic resin, polybutadiene etc. are included to enhance the utility of the insulation materials.

This application is a division of application Ser No. 418,311, filed Sept. 15, 1982, now U.S. Pat. No. 4,507,165.

BACKGROUND OF THE INVENTION

1. Field of Use

This invention relates to elastomeric insulation material especially suited for insulating rocket motors. This invention, more particularly, relates to such an elastomeric insulation material that is free of asbestos and, yet, performs as well or better than analogous insulation material containing asbestos. This invention, still more particularly, relates to such elastomeric insulation materials that contain char forming organic fiber as a low density filler thereof.

2. Prior Art

Elastomer insulation materials comprising asbestos have long been employed within rocket motor cases including such portions thereof as their blast tubes. This invention relates to insulation materials suited to this purpose but which are advantageously free of asbestos.

OBJECTS OF THE INVENTION

It is an object of this invention to provide low density, elastomeric insulation materials for rocket motors.

It is an object of this invention to provide such elastomeric insulation materials in which certain char forming organic particulate replaces asbestos.

It is an object of this invention to provide such asbestos free elastomeric insulation materials that can exhibit certain important properties as least as good as insulation materials having asbestos.

It is an object of this invention to provide methods for compounding and use of these elastomeric insulation materials.

These and other objects are achieved in accordance with this invention; these practices are described more fully in the following together with the present manner in which such objects are accomplished.

As used in the following description of this invention, the term "case wall insulation" refers to a layer or layers of material bonded to the internal wall of the rocket motor case to protect the case from the hot combustion processes occurring during the functioning of the rocket motor. Compositions A, B, C, D (Table V) are suitable materials for this application.

The term "blast tube insulation" in the following refers to material used to line the internal diameter of the blast tube of a rocket. The term "blast tube" refers to the conduit that conveys combustion products of the motor to the nozzle of the rocket. In some rocket motors, due to missile design, the nozzle cannot be connected directly to the rocket motor thereby requiring such a "blast tube." The blast tube lining protects this tube from the hot combustion gases of the rocket motor. Composition C in Table V is suitable for preparing certain blast tube liners.

The nature of specific blast tube insulators, as well as case wall insulators, depends on both mass flux, in the area of application, and burning duration of the rocket motor.

BRIEF SUMMARY OF THE INVENTION

The non-asbestos elastomeric insulation material of this invention comprises 100 parts by weight of a crosslinkable elastomer polymer and between about 10 and 100 (more preferably between about 15 and 75) parts by weight of a char forming organic particulate selected from cotton flock, Sisal or a combination of cotton flock and Sisal.

Among the crosslinkable elastomeric polymers suitable for this invention are an ethylene propylene diene monomer rubber (EPDM) and chlorosulfonated polyethylene rubber. The preferred organic fiber is cotton flock.

DETAILED DESCRIPTION OF THE INVENTION

The elastomer insulation materials of this invention serve such uses as case wall and blast tube insulation for rocket motors. In addition to crosslinkable elastomer polymer, the insulation materials comprise char forming organic particulates such as cotton flock, or Sisal or Sisal and cotton flock as a low density filler. Cotton flock is the preferred char forming organic fiber.

Cotton flock can be obtained from the textile and garment industries. Cotton flock is a short fiber cotton produced by chopping cotton fabric. Poorer grades of cotton flock is obtained from used fabrics.

Cotton flock suitable for this invention includes that with a density between about 1.5 and 1.7 grams per cubic centimeter, more preferably about 1.6 grams per cubic centimeter with mesh sizes ranging between about 10-200 mesh. Fiber diameters are between about 15 and 20 microns, e.g. 17 microns. Ordinarily, undyed or white cotton flock is preferred in this invention.

Generally, the cotton flock (or other such char forming organic fiber e.g. Sisal, a hard fiber obtained from plants of the Amaryllidacene family) is employed in amounts of between about 10 and 100 parts by weight per 100 parts by weight of the elastomer polymer (phr). A range between about 25 and 75 is particularly suitable for most embodiments of this invention.

Use of cotton flock in the insulation materials as discussed in the following yields materials with notable erosion resistance, in some instances even higher than that of analogous asbestos containing elastomer insulation materials. For example, the erosion rate may be as low as 18 mils/sec at flow rates of 1.49 lbs/sec. in.² compared to 28 mils/sec for the asbestos containing material at this flow rate.

This invention is not limited to any particular elastomer polymer. As long as the polymer is crosslinkable, the advantages of this invention should be obtainable. Exemplary polymers, however, are chlorosulfonated polyethylene and ethylene propylene diene monomer (EPDM), both of which are commercially available. Specific suitable EPDM polymers are available as Nordel® 40 from Dupont, Royalene® 100 from Uniroyal, Epsyn® 4506 from Copolymer and Vistalon® 2504 from Exxon.

Preferred EPDM polymers have the following properties:

Density, g/cc 0.85 to 0.865

Mooney, ML-4 @ 212 F 25 to 60

Brittle Point, °F. -90 F.

Hardness, Shore A 30 to 90

Tensile Strength(gumstock), psi 500 to 1000

A specific suitable chlorosulfonated polyethylene is Hypalon LD-999 from Dupont.

The chlorosulfonated polymers used in this invention are preferably cured by a starch/magnesia curing system. Advantageously, the starch in this system also acts as a coolant in that it decomposes to water which, as known, has a high heat of vaporization. Between about 10 and 150 phr of the starch are employed with the chlorosulfonated polyethylene, more preferably between about 20 and 60 phr. The magnesium oxide in these embodiments is employed at between about 1 and 15 phr, more preferably about 1 and 10 phr.

In addition to the starch magnesia curing system, an accelerator is preferably employed with the chlorosulfonated polyethylene. Sulfur accelerators are preferred. An exemplary sulfur accelerator that is commercially available is Tetrone A from Dupont. The accelerator is typically used at between about 0.5 and 5 phr.

The EPDM polymer is preferably cured with a peroxide such as dicumyl peroxide or a t-butyl peroxy compound. These compounds are employed with the EPDM at between about 0.5 and 5 phr.

Silica is an exemplary inorganic filler which may be used in the insulation materials of this invention. Generally, the silica is employed at between about 5 and 80 phr, more usually between about 10 and 50 phr. Other inorganic fillers include antimony oxide which can be used in providing flame retardance to the insulation materials of this invention. The antimony oxide is preferably employed at between about 5 and 60 phr, more preferably about 10 and 35 phr.

In addition to inorganic particulate, the insulation materials may have additional organic additives to enhance the properties of the insulation. For example, chlorinated organic compounds can be used with antimony oxide or hydrated alumina to further enhance flame retardance of EPDM insulation materials. An exemplary chlorinated hydrocarbon for this purpose is Dechlorane® flame retardant. The organic flame retardant is typically used at between about 10 and 80 phr, more preferably 15 and 65 phr.

Liquid polybutadiene is another organic material which is suitably employed in the elastomer materials of this invention. The liquid polybutadiene can increase erosion resistance as well as reduce stiffness in EPDM insulation materials of this invention. A typical level is between about 1 and 50 phr, more preferably 5 and 20 phr of the liquid polybutadiene. An exemplary liquid polybutadiene is Butarez NF from Phillips Petroleum. Moreover, such organic particulate as that derived from phenolic resins can be used advantageously as a replacement for silica. Such a replacement limits visible signature of the insulation material combustion products. The phenolic resin particulate is employed typically between about 30 and 120 phr for increasing char formation and enhance erosion resistance, particularly in chlorosulfonated polyethylene insulation materials of this invention. Exemplary phenolic resin products for this purpose are Resinox® materials from Monsanto.

The elastomeric insulation materials of this invention may be from flexible to rigid using ingredients as above described. Moreover, even higher levels of particulate up to 50% by weight or more can be used for modifying the modulus as desired for particular applications.

Set forth in Tables A, B and C below are exemplary formulations of insulation materials of this invention. Advantageously, specific cured elastomer insulators can be selected to have high erosion resistance comparable or better than their asbestos containing analogs as well as desirable thermal and mechanical properties including bonding capacity to standard propellants and bonding agents.

                  TABLE A                                                          ______________________________________                                         Ingredient          Parts by Weight                                            ______________________________________                                         Chlorosulfonated Polyethylene                                                                      100                                                        Starch              30-50                                                      Magnesia             1-10                                                      Phenolic Resin       80-120                                                    Cotton Flock        30-50                                                      Accelerator         0.5-5                                                      ______________________________________                                    

Insulation materials of this embodiment A has superior erosion resistance.

                  TABLE B                                                          ______________________________________                                         Ingredient          Parts by Weight                                            ______________________________________                                         Chlorosulfonated Polyethylene                                                                      100                                                        Magnesium oxide      1-10                                                      Accelerator         0.5-5                                                      Cotton Flock        30-80                                                      Starch              30-50                                                      Hydrated silica     10-30                                                      ______________________________________                                    

The insulation materials of this embodiment B have good erosion resistance and, advantageously, do not adsorb significant amounts of low polarity plasticizer from propellants containing the same.

                  TABLE C                                                          ______________________________________                                         Ingredient         Parts by Weight                                             ______________________________________                                         EPDM               100                                                         Crosslinking Agent  1-5                                                        Organic Flame Retardant                                                                           20-60                                                       Inorganic Flame Retardant                                                                         10-40                                                       Cotton Flock       10-60                                                       Liquid Polybutadiene                                                                               0-15                                                       ______________________________________                                    

Insulations of this embodiment C are especially suited to case wall or blast tube insulation in view of flame retarding and physical and thermal properties.

                  TABLE D                                                          ______________________________________                                         Ingredient      Parts by Weight                                                ______________________________________                                         EPDM            100                                                            Crosslinking Agent                                                                             1-5                                                            Cotton Flock    20-80                                                          Hydrated Silica 10-30                                                          ______________________________________                                    

Insulators of this embodiment D of this invention are desirably employed as flexible low density insulators having superior erosion, mechanical and thermal properties as well as bond strengths.

Compounding of precursors to the insulation materials of this invention is at temperatures below those which cure the elastomer polymer and permit loss of compounding ingredients. Normally, these temperatures are below about 250° F. for EPDM Normally, these temperatures are below about 250° F. for EPDM compounds and below about 200° F. or even 150° F. for chlorinated polyethylene compounds. Conventional mixing and milling equipment can be used in the compounding.

The insulation material of this invention can be applied to motor cases by wrapping a "bladder mandrel" with calendered sheets of the insulator. The bladder is then inserted into the case and inflated. The inflated bladder forces the insulation against the motor case where it consolidates under pressure. The assembly, with inflated bladder, is then placed in an oven where the insulator is cured. Oven temperature of 300° F. to 350° F. are commonly used. For EPDM cured with peroxide, a minimum temperature of about 310° F. is usually required. After the insulator is cured, the bladder is removed leaving an insulated motor case. It is often advantageous to use primers on metal case walls to enhance bonding of the elastomeric insulator. Primers such as Chemlok 233 or a combination of Chemlok 205 and 234B (products of Hughson Division of Lord Corporation) can be used.

Alternative to the use of the aforedescribed inflatable mandrel technique, the insulation can be molded in matched metal dies for subsequent bonding to the rocket motor case.

Moreover, the insulation formulations can be adapted to the process of Ser. No. 378,588 filed May 17, 1982 (incorporated herein by reference) which utilizes ribbon material in making precision rocket motor case insulation.

The following examples further illustrate aspects of this invention. The illustration by way of these examples is not intended to limit the scope of this invention, but, rather, to demonstrate its varied practice.

EXAMPLE 1

The following formulation (Table I) and procedures are suitable making an elastomer insulation material of this invention. The insulation material is for rocket motor case insulators.

                  TABLE I                                                          ______________________________________                                                                             Weight                                     Components                                                                              Ingredients         phr    Percent                                    ______________________________________                                         1        Chlorosulfonated    100    45.87                                               Polyethylene.sup.(a)                                                  2        Magnesium Oxide.sup.(b)                                                                            6.0    2.75                                       3        Dipentamethylene thiurum hexa                                                                      2.0    0.92                                                sulfide.sup.(c)                                                       4        Cotton flock.sup.(d)                                                                               50.0   22.94                                      5        Corn starch.sup.(e) 40.0   18.35                                      6        Hydrated silica.sup.(f)                                                                            20.0   9.17                                       ______________________________________                                          .sup.(a) Hypalon LD999 from E. I. Dupont                                       .sup.(b) Activated Powder, C. P. Hall Co.                                      .sup.(c) Tetron A from E. I. Dupont                                            .sup.(d) Grade 4128 from Danberg Chemical Co.                                  .sup.(e) American Maize Products Co.                                           .sup.(f) HiSil 233 from PPG Industries, Inc.                             

A first batch of insulation compound from the components of Table I is compounded on a cooled roll mill (Farrel Differential Roll Mill) as follows at temperatures below 200° F.

    ______________________________________                                         Order of                                                                       Addition     Component Milling Time.sup.(g)                                    ______________________________________                                         First        1         3-5        minutes                                      Second       2         2-3        minutes                                      Third        3         2-3        minutes                                      Fourth       5         5-6        minutes                                      Fifth        6         5-6        minutes                                      Sixth        4         13-15      minutes                                      ______________________________________                                          .sup.(g) includes ingredient addition time                               

A second batch of insulation compound from the components of Table I is compounded as follows in a Baker-Perkins mixer with a final temperature below about 150° F.

    ______________________________________                                         Order of                                                                       Addition      Component Mix Time                                               ______________________________________                                         First         1         10                                                     Second        6         12                                                     Third         4         12                                                     Fourth        5         5                                                      Fifth         2 and 3   15                                                     ______________________________________                                    

After each of the batches is mixed and has cooled to room temperature, it is stored in polyethylene bags to prevent contamination.

The following properties are obtainable using the above compounds using either of these compounding procedures followed by a cure at 307° F. for thirty minutes.

    ______________________________________                                         Physical Properties                                                                              Laboratory                                                                             Manu-                                                                  Scale   facturing                                                              Mixing  Scale Mixing                                         ______________________________________                                         1.  Tensile Properties                                                             (ASTM D-412-66 after                                                           30 minutes at 307° F.)                                                  (i) Ultimate Tensile Strength                                                  PSI                                                                            With Fibers         1988      1700                                             Against Fibers      1476                                                       Ultimate Elongation, percent                                                   With Fibers         30        40                                               Against Fibers      80                                                     2.  Hardness, Share A   95                                                         (ASTM D-314-28)                                                            3.  Density, lb/in.sup.3                                                                               0.0498    0.0492                                       ______________________________________                                    

Cured elastomer of this example is suited for for use with rocket motor propellants having hydroxy or carboxy terminated polybutadiene as a binder material. Due to its stiffness, it is advantageously used as a bonded case wall insulation or, due to its low affinity to many plasticiziers, as a barrier film for other insulators. Post cure of ten (10) hours at 250° F. followed by grit blasting and then solvent cleaning (chloroethylene) is recommended for improved bonding. Specific applications may require a propellant/ insulation bond compatibility study.

EXAMPLE 2

The following formulation (Table II) and procedures are suited for making elastomer material of this invention for rocket motor case insulation.

                  TABLE II                                                         ______________________________________                                                                             Weight                                     Components                                                                              Ingredient          phr    Percent                                    ______________________________________                                         1        Chlorosulfonated Polyethylene.sup.(a)                                                              100    34.73                                      2        Magnesium Oxide.sup.(b)                                                                             6      2.08                                      3        Starch.sup.(c)       40    13.89                                      4        Cotton flock.sup.(d)                                                                                40    13.89                                      5        Phenolic Resin.sup.(e)                                                                             100    34.72                                      6        Dipentamethylenethiurium-                                                                           2      0.69                                               hexasulfide.sup.(f)                                                                                       100.00                                     ______________________________________                                          .sup.(a) Hypalon LD999 from E. I. Dupont de Nemours                            .sup.(b) Activated Powder, C. P. Hall Co.                                      .sup.(c) Cornstarch, American Maize Products Co.                               .sup.(d) Grade 4128 from Danberg Chemical Co.                                  .sup.(e) Resinox RC 755 from Monsanto                                          .sup.(f) Sulfad from R. T. Vanderbilt or Tetrone A from E. I. Dupont de        Nemours                                                                  

A batch of elastomer insulator compound is prepared on a cooled roll mill from the components of Table II at temperatures below 200° F. as follows:

    ______________________________________                                         Order of                                                                       Addition     Component Milling time.sup.(g)                                    ______________________________________                                         First        1         3-5        minutes                                      Second       2         2-3        minutes                                      Third        6         2-3        minutes                                      Fourth       3         5-6        minutes                                      Fifth        5         6-9        minutes                                      Sixth        4         13-15      minutes                                      ______________________________________                                          .sup.(g) Includes ingredient addition time.                              

After this batch is mixed and cooled to room temperature, it is stored in polyethylene bags to prevent contamination. The following properties are obtainable from curing compounds of this Example 2 at a termperature of 307° F. for thirty minutes.

    ______________________________________                                         Physical Properties                                                                                   Laboratory                                                                     Mixed                                                   ______________________________________                                         1.     Tensile Properties                                                             (ASTM D-412-66 after 30 minutes at                                             340 F.)                                                                        Ultimate Tensile Strength, psi                                                                       2811                                                     With Fibers                                                                    Ultimate Elongation, percent                                                                         20                                                       With Fibers                                                             2.     Hardness, Shore A (ASTM D-314-28)                                                                    95                                                3.     Density, lb/in.sup.3  0.0472                                            ______________________________________                                    

The cured elastomer of this example is suited for use in rocket motors having either hydroxy terminated or carboxy terminated polybutadiene bound propellants. Due to its stiffness, the resultant elastomer material is best utilized as a bonded case wall insulation or, blast tube liner. A post cure of ten (10) hours at 250° F. is recommended. Specific applications may require propellant/insulation bond compatibility studies.

EXAMPLE 3

The following formulation (Table III) is used in making an elastomer insulation material of this invention.

                  TABLE III                                                        ______________________________________                                         Components                                                                              Ingredient      phr     Weight Percent                                ______________________________________                                         1        EPDM.sup.(a)    100.0   51.95                                         2        2,5-dimethyl-2,5-di(t-                                                                          2.5     1.30                                                  butylperoxy)hexane.sup.(b)                                            3        Flame retardant.sup.(c)                                                                        40.0    20.78                                         4        Antimony Oxide.sup.(d)                                                                         20.0    10.39                                         5        Cotton Flock.sup.(e)                                                                           20.0    10.39                                         6        Linear Polybutadiene.sup.(f)                                                                   10.0     5.19                                                                          100.00                                        ______________________________________                                          .sup.(a) Nordel 1040 from E. I. Dupont                                         .sup.(b) Varox from R. T. Vanderbilt                                           .sup.(c) Dechlorane Plus 515 from Hooker Chemical                              .sup.(d) Mil-A-51312, Harshaw Chemical Co.                                     .sup.(e) Grade 4128 from Danberg Chemical Company                              .sup.(f) Butarez N. F. from Phillips Petroleum Co.                       

A first batch of insulation precursor material from the components in Table III is compounded at temperatures below 250° F. on a cooled roll mill as follows:

    ______________________________________                                         Order of                                                                       Addition     Component Milling Time.sup.(g)                                    ______________________________________                                         First        1         1-3        minutes                                      Second       2         2-3        minutes                                      Third        3         10-12      minutes                                      Fourth       4         5-6        minutes                                      Fifth        6         6-9        minutes                                      Sixth        5         13-15      minutes                                      ______________________________________                                          .sup.(g) Includes ingredient addition time.                              

A second batch is compounded in a Baker Perkins Mixer from the components of Table III at temperatures below 250° F. as follows:

    ______________________________________                                         Order of                                                                       Addition   Component Mix Time (Minimum)                                        ______________________________________                                         First      1         10 minutes                                                Second     3         15 minutes                                                Third      4          5 minutes                                                Fourth     6         Until well incorporated                                   Fifth.sup.(1)                                                                             5         16 minutes                                                Sixth      2         15 minutes                                                ______________________________________                                          .sup.(1) Cotton Flock may be added incrementally to facilitate                 incorporation into the mix.                                              

The following physical properties are obtainable from curing either of the above compounds of this Example 3 at a temperature of 340° F. for thirty (30) minutes.

    ______________________________________                                         Physical Properties                                                                                   Laboratory                                                                     Mixed                                                   ______________________________________                                         1.     Tensile Properties                                                             (ASTM D-412-66 after 30 minutes                                                at 340 F.)                                                                     Ultimate Tensile Strength, psi                                                                       484                                                      With Fibers                                                                    Ultimate Elongation, percent                                                                         63                                                       With Fibers                                                             2.     Hardness, Shore A (ASTM D-314-28)                                                                    70                                                3.     Density, lb/in.sup.3  0.0413                                            ______________________________________                                    

The cured elastomer of this example may be used for floaters, case liner or insulation material for rocket motors. A post cure of ten (10) hours at 250° F. is recommended. Specific applications may require study of compatibility with propellant formulations. Epoxy based and polybutadiene-based adhesives may be used for adherence to steel or to the cured elastomer itself. In addition, the uncured elastomer can be used as a binder in such circumstances.

EXAMPLE 4

The following formulation (Table IV) and procedures are suited for making an elastomer insulation material of this invention.

                  TABLE IV                                                         ______________________________________                                                                           Weight                                       Component Ingredients     phr     Percent                                      ______________________________________                                         1         EPDM.sup.(a)    100.0   57.971                                       2         2,5-dimethyl-2,5-di(t-                                                                         2.5      1.449                                                 butylperoxy)hexane.sup.(b)                                           3         Cotton Flock.sup.(c)                                                                           50.00   28.986                                       4         Hydrated silica.sup.(d)                                                                        20.00   11.594                                                                         100.000                                      ______________________________________                                          .sup.(a) Nordel 1040 from DuPont                                               .sup.(b) Varox from R. T. Vanderbilt                                           .sup.(c) Grade 4128 from Danberg Chemical Co.                                  .sup.(d) HiSil 233 from PPG Industries, Inc.                             

A first batch is compounded from the components of Table IV on a cooled roll mill (Farrel Differential Roll Mill) at temperatures below 200° F. as follows:

    ______________________________________                                         Order of                                                                       Addition     Component Milling.sup.(g)                                         ______________________________________                                         First        1         1-3        minutes                                      Second       2         2-3        minutes                                      Third        3         10-12      minutes                                      Fourth       4         13-15      minutes                                      ______________________________________                                          .sup.(g) Includes ingredient addition time.                              

A second batch from the components of Table IV is compounded in a Baker-Perkins mixer with a final temperature below 200° F.

    ______________________________________                                         Order of                                                                       Addition    Component Mix Time, (Minimum)                                      ______________________________________                                         First       1         10 minutes                                               Second.sup.(1)                                                                             3         12 minutes                                               Third.sup.(1)                                                                              4         30 minutes                                               Fourth      2         15 minutes                                               ______________________________________                                          .sup.(1) HiSil 233 and Cotton Flock are added incrementally to facilitate      incorporation into the mix.                                              

The following physical properties are obtainable from curing either of the above compounds of this Example 4 at temperatures of about 340° F. for thirty minutes.

    ______________________________________                                         Physical Properties                                                                                   Laboratory                                                                     Mixed                                                   ______________________________________                                         1.     Tensile Properties                                                             (ASTM D-412-66 after 30 minutes at                                             340 F.)                                                                        Ultimate Tensile Strength, psi                                                                       642                                                      With Fibers                                                                    Against Fibers                                                                 Ultimate Elongation, percent                                                                         40                                                       With Fibers                                                                    Against Fibers                                                          2.     Hardness Shore A (ASTM D-314-28)                                                                     80                                                3.     Density, lb/in.sup.3  0.0383                                            ______________________________________                                    

The cured elastomer of this example may be used as floater, case liner or insulation material for rocket motor cases. Both carboxy terminated and hydroxy terminated polybutadiene bound propellants can be used with the elastomer material of this example. Adhesives suited for binding the elastomer material to steel or itself include epoxies, Butarez CTL-based adhesives. The formulation is also self binding during cure. A post cure of ten (10) hours at 250° F. is recommended before contact with propellant. Specific propellant formulations may require insulator/propellant bond compatibility studies.

TEST RESULTS

Table V below illustrates results obtainable from cured elastomer materials made in accordance with this invention and prior art compositions containing asbestos. In Table V, formulation A is compounded using procedures of Example 3, B procedures of Example 4, C procedures of Example 2 and D procedures of Example 1. Formulations E through H are conventional elastomer materials used in rocket motor cases and contain asbestos.

                                      TABLE V                                      __________________________________________________________________________     EROSION, MECHANICAL, THERMAL PROPERTIES AND DENSITY OF EXEMPLARY               INSULATORS COMPARED WITH ASBESTOS COMPOSITIONS                                              A   B   C   D   E   F   G   H                                     __________________________________________________________________________     Ingredient, phr                                                                EPDM.sup.(a) 100.0                                                                              100.0       100.0                                                                              100.0                                                                              100.0                                     2,5-dimethyl-                                                                               2.5 2.5         2.5 2.5 7.5                                       2,5(di-t-butyl-                                                                peroxy)-                                                                       hexane.sup.(b)                                                                 Flame retardent.sup.(c)                                                                     40.0            40.0                                                                               40.0                                          Antimony Oxide                                                                              20.0            20.0                                                                               20.0                                          Polybutadiene.sup.(d)                                                                       10.0                10.0                                          Cotton Flock 20.0                                                                               50.0                                                                               40.0                                                                               50.0                                                  Silica.sup.(e)   20.0    20.0                                                  Chlorosulfonated     100.0                                                                              100.0                                                 Polyethylene.sup.(f)                                                           Magnesia             6.0 6.0                                                   Starch               40.0                                                                               40.0                                                  Dipentamethylene     2.0 2.0                                                   thiurum hexa                                                                   sulfide.sup.(g)                                                                Phenolic resin.sup.(h)                                                                              100.0                                                     Asbestos.sup.(i)             20.0                                                                               20.0                                                                               100.0                                     Phenolic Resin                           100.0                                 Asbestos Felt                            300.0                                 Polybutadiene.sup.(j)                10.0                                      Erosion/Decomposition,                                                         mils/sec                                                                       0.245 lbs/sec                                                                               10  8.5 7   10  11  12      7                                     in.sup.2 *                                                                     0.141 lbs/sec                                                                               13  9-11                                                                               5   13  11  14      11                                    in.sup.2 **                                                                    1.49 lbs/sec 40  400 18  62  56  --  28.0                                                                               28.0                                  in.sup.2 **                                                                    Mechanical Properties                                                          (77 F, 20 in./min X-Head)                                                      m, %         63  40  20  30  63  284 29                                        m, psi       484 642 2710                                                                               1988                                                                               360 455 2279                                                                               38000                                 Density, lb/in.sup.3                                                                        0.0413                                                                             0.0387                                                                             0.0457                                                                             0.0492  0.0428                                                                             0.046                                                                              0.061                                 Rex Hardness 70  80  95  95  80  75  85  100                                   Thermal Properties                                                             Expansion,                                                                     in./in./deg F. × 10.sup.-5                                               o            7.7 6.2 2.3 4.7 --  9.1 --  --                                    1            25.1                                                                               24.5                                                                               14.8                                                                               16.7                                                                               24.0                                                                               27.3                                                                               --  27.0                                  Conductivity,                                                                               0.13                                                                               0.10                                                                               0.11                                                                               0.15                                                                               0.13                                                                               0.12                                                                               0.2 0.16-0.3                              BTU/hr(ft.sup.2)/deg                                                           F/ft                                                                           Tg deg F     -74 -62 3   14      -72     77                                    __________________________________________________________________________      *From twoinch apparatus                                                        **From sixinch material test motor                                             .sup.(a) Nordel 1040 ®-                                                    .sup.(b) Varox ®-                                                          .sup.(c) Dechlorane Plus ®-                                                .sup.(d) Butarez NF ®-                                                     .sup.(e) HiSil 233 ®-                                                      .sup.(f) Hypalon LD999 ®-                                                  .sup.(g) Sulfads ®-                                                        .sup.(h) Rexinox RC 755 ®-                                                 .sup.(i) Plastibest 20 ®-                                                  .sup. (j) Butarez CTL II ®-                                          

Table VI shows properties of elastomers made generally using procedures of Example 3 against asbestos containing analogs. The formulations listed in Table VI, i.e. A1, A2, A3, A4, A5 and A6, are variants of formulation A of Table V.

                                      TABLE VI                                     __________________________________________________________________________                  A1 E1  A2 A3 A4  A5 E2 A6                                         __________________________________________________________________________     Ingredient, phr                                                                EPDM.sup.(a) 100.0                                                                             100.0                                                                              100.0                                                                             100.0                                                                             100.0                                                                              100.0                                                                             100.0                                                                             100.0                                      2,5-dimethyl-2,5-                                                                           2.5                                                                               2.5 2.5                                                                               2.5                                                                               2.5 7.5                                                                               2.5                                                                               2.5                                        (di-t-butyl-                                                                   peroxy hexane.sup.(b)                                                          Sisal, 1/4" Fiber                                                                           20.0                                                                              --  -- 80.0                                                                              --  -- -- --                                         Cotton Flock -- --  20.0                                                                              -- 20.0                                                                               20.0                                                                              -- --                                         Antimony Oxide                                                                              20.0                                                                              20.0                                                                               20.0                                                                              20.0                                                                              20.0                                                                               20.0                                                                              20.0                                                                              20.0                                       Flame Retardent.sup.(c)                                                                     40.0                                                                              40.0                                                                               40.0                                                                              40.0                                                                              40.0                                                                               40.0                                                                              40.0                                                                              40.0                                       Polybutadiene.sup.(d)                                                                       10.0                                                                              10.0                                                                               10.0                                                                              -- --  10.0                                                                              -- 10.0                                       Asbestos     -- 20.0                                                                               -- -- --  -- 20.0                                                                              --                                         Cotton Flock + A-172                                                                        -- --  -- -- --  -- -- 20.0                                       (Silane Coupling Agent)                                                        Erosion/Decompo-                                                                            11 12  10 14 17  7.5                                                                               11 9                                          sition                                                                         (Mils/Sec)                                                                     Mechanical Properties                                                          (77 F, 20 in./min X-head)                                                      m, %         40 284 63 20 60  40 63 73                                         m, psi       313                                                                               455 484                                                                               901                                                                               359 878                                                                               360                                                                               592                                        __________________________________________________________________________      .sup.(a) Nordel 1040 ®-                                                    .sup.(b) Varox ®-                                                          .sup.(c) Dechlorane Plus ®-                                                .sup.(d) Butarez NF ®-                                               

Table VII shows properties of elastomers made generally in accordance with procedures of Example 4. The formulations listed in Table VII, i.e. B1, B2, B3, B4 and B5, are variants of formulation B in Table V.

                  TABLE VII                                                        ______________________________________                                         Ingredient, phr B1     B2      B3   B4    B5                                   ______________________________________                                         EPDM.sup.(a)    100.0  100.0   100.0                                                                               100.0 100.0                                2,5 dimethyl-2,5                                                                                2.5    2.5     2.5  2.5   2.5                                 (dit-butylperoxy)                                                              hexane.sup.(b)                                                                 Silica.sup.(c)  35.0   35.0    20.0 20.0  40.0                                 Cotton Flock    --     --      10.0 50.0  50.0                                 Acetylene Black  0.5   --                                                      (100% Comp.)                                                                   Sym.di-beta-            3.0                                                    napthyl-p-                                                                     phenylenedi-                                                                   amine.sup.(d)                                                                  Erosion/Decompo-                                                                               12.0   15.0    11.0  8.5   8.3                                 sition                                                                         (Mils/Sec)*                                                                    Mechanical Properties                                                          (77 F., 20 in./min X-Head)                                                     m, %             845   1258    540   40    30                                  m, psi          1728    812    697  642   898                                  ______________________________________                                          *0.245 lb/secin.sup.2                                                          .sup.(a) Nordel 1040 ®-                                                    .sup.(b) Varox ®-                                                          .sup.(c) HiSil 233 ®-                                                      .sup.(d) Agerite White ®-                                            

Table VIII shows properties of elastomers made generally in accordance with Example 2 against analogous asbestos containing compositions. The formulations listed in Table VIII, i.e. C1, C2, C3, C4, C5 and C6 are variants of formulation C in Table V.

                                      TABLE VIII                                   __________________________________________________________________________                  C1 C2 C3 C4 C5 C6 G  E  H                                         __________________________________________________________________________     Ingredient, phr                                                                Chlorosulfonated                                                                            100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                              Polyethylene.sup.(a)                                                           Magnesia     6.0                                                                               4.0                                                                               6.0                                                                               6.0                                                                               6.0                                                                               6.0                                                Dipentamethylene                                                                            2.0                                                                               2.0                                                                               2.0                                                                               2.0                                                                               2.0                                                                               2.0                                                thiurum hexa                                                                   sulfide.sup.(b)                                                                Starch, Corn 40.0                                                                              10.0                                                                              40.0                                                                              100.0                                                                             40.0                                                                              40.0                                               Cotton Flock 40.0                                                                              -- 40.0                                                                              40.0                                                                              100.0                                                                             --                                                 Phenolic Resin.sup.(c)                                                                      100.0                                                                             -- 60.0                                                                              60.0                                                                              60.0                                                                              100.0                                              Sisal, 1/4" Fiber           40.0                                               EPDM.sup.(d)                   100.0                                                                             100.0                                        2,5 dimethyl-2,5-              7.5                                                                               2.5                                          di(t-butylperoxy)                                                              hexane.sup.(e)                                                                 Asbestos                       100.0                                                                             20.0                                         Linear polybuta-               10.0                                                                              --                                           diene.sup.(f)                                                                  Antimony Oxide                    20.0                                         Flame retardent.sup.(g)              40.0                                      Asbestos Felt                        300                                       Phenolic Resin                       100                                       Erosion/Decomposition                                                                       6.7                                                                               -- 8. 7.2                                                                               9. 12 -- 11 7                                         Rate, mils/sec at:                                                             0.245 lbs/sec in.sup.2                                                         Mechanical Properties                                                          (77 F, 20 in./min X-head)                                                      m, %         20 475                                                                               50 10 10 10 29 63 1.15                                      m, psi       2811                                                                              3006                                                                              1972                                                                              2426                                                                              3132                                                                              3018                                                                              2279                                                                              360                                                                               45000                                     __________________________________________________________________________      .sup.(a) Hypalon LD999 ®-                                                  .sup.(b) Tetron A ®-                                                       .sup.(c) Resinox 755 ®-                                                    .sup.(d) Nordel 1040 ®-                                                    .sup.(e) Varox ®-                                                          .sup.(f) Butarez CTL II ®-                                                 .sup.(g) Dechlorane Plus ®-                                          

Table IX shows results of plasticizer absorption tests of elastomers of this invention compared to an analogous asbestos containing compositions wherein the formulations for A, B, C, D and F are shown in Table V.

                  TABLE IX                                                         ______________________________________                                                      Plasticizer Absorption After                                                   120 Hour, Percent                                                 Insulator                                                                             Test Temp., F.                                                                             CLO.sup.(1)                                                                             IDP.sup.(2)                                                                          DOA.sup.(3)                                                                           3GH.sup.(4)                           ______________________________________                                         F      77          67       119   10     42                                           145         192      130   34     60                                    A      77          95       88    -1.7   15                                           145         124      182   -2.7   57                                    B      77          62       68    4      23                                           145         125      86    8      43                                    C      77                   4            5                                            145                  16           22                                    D      77          1.5      7     8      9                                            145         9        21    28     29                                                 Polarity Increase                                                 ______________________________________                                          .sup.(1) Circo Light Oil ®-                                                .sup.(2) Isodecyl Pelargonate                                                  .sup.(3) Dioctyl Adipate                                                       .sup.(4) Flexol 3GH ®-                                               

Table X shows results of bonding of elastomer materials of this invention (A, B, C and D as in Table V) in the presence or absence of A-128, a liner material prepared as in Example 5 (Table XII) to a standard propellant composition containing hydroxy terminated polybutadiene as a binder material. Results from bonding of Composition H (Table V) are also shown.

                  TABLE X                                                          ______________________________________                                                        Tensile Bond Strengths, psi                                     Insulator System                                                                          Test Temp.                                                                               #1        #2     #3                                       ______________________________________                                         D          -65       353(CP)   413(CP)                                                                               416(CP)                                              77        44(M)     18(A)  44(M)                                               165       21(A)     19(A)  10(A)                                   D + A - 128                                                                               -65       489(CP)   381(CP)                                                                               --                                                   77        95(CP)    77(CP)                                                                               107(CP)                                              165       66(CP)    65(CP)                                                                                69(CP)                                  A          -65       475(CP)   566(CP)                                                                               489(CP)                                              77        89(CP)    99(CP)                                                                                94(CP)                                              165       81(CP)    74(CP)                                                                                69(CP)                                  A + A - 128                                                                               -65       485(CP)   378(CP)                                                                               --                                                   77       119(CP)   117(CP)                                                                               107(CP)                                              165       68(M)     85(CP)                                                                                70(M)                                   C          -65       288(A)    268(A)                                                      77        20(A)     11(A)  18(A)                                               165      --         10(A)  5(A)                                    C + A - 128                                                                               -65       559(CP)   483(CP)                                                                               552(CP)                                              77        70(CP)   110(CP)                                                                               105(CP)                                              165       67(CP)    86(CP)                                                                                65(CP)                                  D          -65       358(A)    402(A) 282(A)                                               77        24(A)     28(A)  43(A)                                               165       27(A)    --      27(A)                                   D + A - 128                                                                               -65       534(CP)   485(CP)                                                                               565(CP)                                              77       101(CP)   101(CP)                                                                                98(CP)                                              165       61(CP)    68(CP)                                                                                69(CP)                                  H          -65       424(M)    520(M) --                                                   77        98        89    101                                                  165        71(M)    74(M)  74(M)                                   ______________________________________                                          A = Failed adhesively in bond                                                  CP = Failed Cohesively in propellant                                           M = Mixed failure at the bond and in the propellant                      

EXAMPLE 5

This example illustrates use of elastomer compositions of this invention in the specific application of stress relieving liners (SRL) for end burning or highly stressed internal burning propellant grains. (The principle of SRL is the breaking up of the stresses, normal to the case bonded propellant grains in a rocket motor, into small stress columns that independantly undergo triaxial stress, thus reducing stress-strain fields in the propellant grain.

A SRL has five (5) components. These components are: an insulator, column material (i.e. stress relieving material), separator sheet, migration barrier and a liner that promotes bonding between propellant and insulator materials. Typically, the columns are sized to give between about 30 and 80 percent unbonded area, the number, size and placement determined from stress analysis of the grain to be supported by the SRL.

Proceeding from the case wall to propellant, the SRL of this example has (a) a first insulator, (b) either column material or separator sheet, (c) a second insulator (d) a migration barrier; and (e) a liner. The column material is disk like in confirguration. The first and second insulators comprise material formulated as in Example 4; this insulation material formulation is modified to yield a soft column material from data in Table XI below.

                  TABLE XI                                                         ______________________________________                                         COMPOSITIONS OF COLUMN MATERIAL                                                CANDIDATES RESULTING FROM MODIFICATIONS OF                                     COMPOSITIONS OF EXAMPLE 4                                                                   Exem-                                                             Ingredients, phr                                                                            plary   4A      4B    4C    4D                                    ______________________________________                                         Nordel 1040 (EPDM)                                                                          100.0   100.0   100.0 100.0 100.0                                 Varox         2.5     2.5     2.0   2.0   2.0                                  Cotton Flock 50.0    10.0    10.0  10.0  10.0                                  HiSil 233    20.0    20.0    20.0  15.0  10.0                                  Butarez NF   --      --      20.0  20.0  20.0                                  Mechanical Properties                                                          (20 in./min X-Head                                                             Speed, 77 F.)                                                                  Parallel to Fibers                                                             m, %          40     540     680   700   640                                   m, psi       642     697     493   405   444                                   Perpendicular                                                                  to Fibers                                                                      m, %         --      --      650   690   680                                   m, psi       --      --      443   405   442                                   ______________________________________                                    

Testing of the materials of Table XI results in selection of composition 4D for the desired material of the support column.

The separator sheet is made from an elastomeric silicone material (Cohrlastic® 9360, available from Connecticut Hard Rubber Company) The Cohrlastic® material can vary in thickness, dependant on SRL requirements, but typically ranges between about 0.060 and 0.25 inches, e.g. 0.189 inches.

Two materials are evaluated as the barrier material for the migration barrier. The materials are a composition prepared as in Example 1 and Tuftane TF-310, a polyesterpolyurethane from B. F. Goodrich. Testing shows these materials function essentially equivalently as migration barriers.

The liner is chosen to be a composition as set forth in Table XII below

                  TABLE XII                                                        ______________________________________                                         COMPOSITION OF LINER A-128A                                                    Ingredient         Wt. Percent                                                 ______________________________________                                         Masterbatch            77.00                                                   R-45M.sup.(a)   65.00                                                          Carbon Black (FEF)                                                                             35.00                                                          HX-868.sup.(b)          1.50                                                   A.O. 2246.sup.(c)       0.15                                                   R-45M/TDI*.sup.(d)     21.35                                                   ______________________________________                                          *Curative to polymer to give a 2.0 equivalent NCO:OH ratio.                    .sup.(a) A hydroxy terminated polybutadiene material from Arco Chemical.       .sup.(b) A bonding agent catalyst available from 3M Company.                   .sup.(c) An antioxidant available from American Cyanamid.                      .sup.(d) A blend of (a) and toluene diisocynate from E. I. Dupont de           Nemours & Co.                                                            

Table XIII shows results of using the A-128 with the elastomer compositions of Example 1 and 4 as set forth above in the Example 5.

                  TABLE XIII                                                       ______________________________________                                         BOND DATA BETWEEN LINED WITH A-128A                                            AND PROPELLANT MG-819 (LCA-9843)*                                                         Tensile Bond, psi**                                                                          90 Degree                                             Test Temp., F.                                                                              #1     #2        #3   Peel, pli**                                 ______________________________________                                         -65          642.sup.(a)                                                                           568.sup.(b)                                                                              427.sup.(b)                                                                         85.sup.(b)                                   77          177.sup.(b)                                                                           140.sup.(a)                                                                              177.sup.(b)                                                                         5 to 6.sup.(b)                               165          82.sup.(a)                                                                           138.sup.(b)                                                                               95.sup.(a)                                                                          3.8.sup.(b)                                ______________________________________                                          *88 percent solids with 20 percent Al                                          **0.2/in./min Xhead                                                            .sup.(a) Failed primarily in liner                                             .sup.(b) Failed in propellant                                            

Six-Inch SRL Motor

To verify the applicability of the above non-asbestos SRL system to case bonded, end burning motors, six-inch test motors were fabricated and tested. Fabrication entailed the lining of a six-inch test motor with the SRL system. The procedure for forming the SRL is given in Table XIV. After the SRL was installed in the case, the barrier film (composition of Example 1) was lined with A-128A (Table XII) to a thickness of between 10 and 15 mils. Lining was accomplished by spraying the interior of the SRL with the A-128A diluted with chloroethane (2 to 1 by volume). After flashing the liner two hours (minimum) at 145° F., the SRL insulated case was vacuum cast with a proprietary propellant. The cast propellant grain was cured 96 hours at 145° F. Following grain cure and cool down to 77F, attempts were made to vent the SRL system; however, the SRL was 11.5 inches long, while the grain was only 9 inches long, and thus left over an inch of SRL extending beyond the ends of the grain. Shrinkage of the grain was not sufficient to separate the extended ends of the SRL to affect venting. Cooling the grain to -40° F. was attempted to induce sufficient shrinkage; but this, too, proved unsuccessful. Finally, radial slots were cut in the insulator layer of the SRL down to the separator sheet. The slots (1/4×2 inches) were located approximately 1/4 inch from the aft end of the grain and 1/2 inch from the forward end of the grain and were spaced approximately one inch apart, radially. The slotting operation yielded the desired venting. Dry nitrogen could be easily flowed through the SRL (aft to forward) at 15 psia.

After X-ray of the grain for defects, the forward end of the grain was inhibited with a 3/8 thick layer of inhibitor (see Table XV), which was allowed to cure overnight (16 hours) at 77 F. A 25 gram wafer igniter containing 25 grams of a pyrotectnic ignitor was attached to the aft grain surface, then motor assembly was completed by attaching the forward head and nozzle to the motor.

Post-firing examination revealed an even burnout on the aft grain inhibitor. The insulation was still intact with virgin insulation still remaining over columns and separator sheet, even at the aft end of the SRL lay-up.

                  TABLE XIV                                                        ______________________________________                                         PROCEDURE FOR FORMING                                                          SRL IN SIX-INCH TEST MOTOR                                                     ______________________________________                                         1.   Grit blast I.D. of motor case - clean with 1,1,1-                              Trichloroethane                                                           2.   Prime I.D. of motor case with Chemlok 233                                 3.   Flash Chemlok 233 for 30 minutes miminum at 77 F.                         4.   Wrap bladder mandrel with one layer of 0.030 inch thick                        sheet of a composition prepared as in Example 4.                          5.   Cold flow the layer of step 4 to I.D. of motor case                            using 100 psig nitrogen pressure in bladder.                              6.   Install perforated silicone separator sheet over the                           layer of step 5.                                                          7.   Fill perforations in separator sheet with discs of the                         composition 4D (Table XI) (discs = 0.5 inches in diam-                         eter by 0.2 inches thick)                                                 8.   Wrap bladder mandrel with one wrap of 0.032 inch thick of                      the composition of example 1 followed by 2 wraps of                            0.025 inch thick of the composition of Example 4.                         9.   Insert wrapped bladder into I.D. of motor case - apply                         100 psig nitrogen pressure.                                               10.  Cure, under presdure, for 2.5 hours at 350 F.                             11.  Remove mandrel                                                            12.  Grit blast I.D. of the inner layer 8 prepared from the                         composition of Example 1.                                                 13.  Post cure 9 hours of 250 F.                                               ______________________________________                                    

                  TABLE XV                                                         ______________________________________                                         COMPOSITION AND PROPERTIES INHIBITOR                                           ______________________________________                                         Ingredient      phr      Wt. %                                                 ______________________________________                                         R-45M.sup.(a)   100.000  29.795                                                IDP (Isodecyl   25.000   7.449                                                 Pelargonate).sup.(b)                                                           Mannitol.sup.(c)                                                                               200.000  59.591                                                HX-868.sup.(d)  2.500    0.745                                                 HMDI.sup.(e)    6.600    1.966                                                 A.O. 2246       1.500    0.447                                                 FeAA.sup.(g)     0.025*  0.007                                                                          100.000                                               ______________________________________                                         Mechanical Properties                                                          Test Temp. m, %         m, psi  E, psi                                         ______________________________________                                         -65 F.     144          558     1730                                           -45 F.     127          362     1270                                            77 F.     107          88       304                                            170 F.     51          77       254                                           -116 F.                                                                        T.sub.g                                                                        Thermal Expansion, in./in./°C. 21.7 × 10.sup.-5                   ______________________________________                                          *FeAA content can be adjusted to regulate pot life.                            .sup.(a) A hydroxy terminated polybutadiene available from Arco Chemical       Co.                                                                            .sup.(b) A plasticizer available from Emery Industries.                        .sup.(d) A bonding agent, available from 3M Company.                           .sup.(e) An isocyanate available from Mobby Chemical Company                   .sup.(f) An antioxidant available from American Cyanamid.                

EXPERIMENTAL

Uniaxial mechanical properties of insulators of this Example 5 were obtained in accordance with ASTM method D412-68. Tests were conducted on an Instron Tensile Tester using a crosshead speed of 20 in./min. For propellant mechanical properties, Class "C" type tensile specimens were employed having an effective gauge length of 2.7 inches. Test temperatures and strain rates were varied to yield time-temperature response spectrum.

Triaxial tensile tests were conducted using the four-inch specimens. The specimens used had 0.5-inch diameter columns by 0.188 inches long. Column area was maintained at 50 percent of the total SRL bond surface. Testing was conducted at two different temperatures and strain rates to provide data for stress analysis.

Tensile bond and 90 degree peel bond data were obtained by pulling the appropriate specimens on an Instron Tensile Tester at crosshead speeds of 0.2-in./min. Tensile bond specimens were 1.5 inch diameter triaxial specimens (tensile buttons) containing layers of insulator and propellant. Peel specimens consisted of one inch wide propellant blocks (1×1×3inches) with insulator bonded to one face. Bonding was effected by casting and curing propellant onto lined (with A×128A) glass reinforced panels (6x6 inches) of insulators. 

What is claimed is:
 1. A non-asbestos elastomeric insulation material in a shape of an interior portion of a rocket motor, said insulation material consisting essentially of:(A) 100 parts of a crosslinkable elastomer comprising EPDM having a Mooney Viscosity, ML-4 at 212° F. between about 25 and 60; (B) About 10-60 parts by weight of a char-forming organic fiber selected from the group consisting of cotton flock, Sisal and a combination of cotton flock and Sisal; (C) About 10-40 parts by weight of an inorganic flame retardant selected from silica, antimony oxide and hydrated alumina; (D) About 20-60 parts by weight of an organic flame retardant selected from chlorinated organic compounds; (E) About 10-5 parts by weight of a peroxide crosslinking agent; and (F) About 0-15 parts by weight of liquid polybutadiene.
 2. The insulation material in accordance with claim 1, wherein said char-forming fiber consists essentially of cotton flock.
 3. The insulation material in accordance with claim 2, wherein said shape comprises that of a rocket motor blast tube.
 4. The insulation material in accordance with claim 2, wherein said shape comprises that of a rocket motor case wall.
 5. The insulation material in accordance with claim 3, wherein said inorganic flame retardant consists essentially of antimony oxide.
 6. The insulation material in accordinace with claim 4, wherein said inorganic flame retardant consists essentially of antimony oxide.
 7. A non-asbestos elastomeric insulation material in a shape of an interior portion of a rocket motor case, said insulation material consisting essentially of: (A) 100 parts by weight chlorosulfonated polyethylene; (B) About 10-100 parts by weight of a char-forming organic fiber selected from cotton flock, Sisal and a combination of cotton flock and Sisal; (C) About 10-150 parts by weight starch; (D) About 5-60 parts by weight antimony oxides; (E) About 10-80 parts by weight of an organic flame retardant selected from chloronated hydrocarbons; (F) About 1-10 parts by weight magnesium oxide; and (G) About 0.5-5 parts by weight of an accelerator.
 8. The insulation material in accordance with claim 7, wherein said char-forming organic fiber comprises cotton flock.
 9. The insulation material in accordance with claim 8, wherein said shape comprises that of a rocket motor case wall.
 10. The insulation material in accordance with claim 8, wherein said accelerator is a sulfur accelerator. 